There is much to learn about the various aspects of frost protection. UC Davis biometerology program provides explanation and training in English and Spanish on their website.
Monthly Archives: December 2014
Watch what four Nobel Laureates from UC Berkeley have to say about collaborative research
Efforts continue to emphasize the absolute need for an all inclusive task-force to deal with the ambrosia beetles’ infestations of avocados in California and other countries around the world. The resistance-reluctance by CAC and the researchers who are being funded need to drop the personality first attitude and allow for a solution driven collaborative effort by individuals and groups who also care.
The expanded task-force will become a reality in the near future; it must! Of course the inclusion of the UCR scientists and the assistance by CAC (notice that I did not write “directed” by CAC; it is not only a California problem and therefore CAC should not insist on owning the effort!).
I believe the segment from the conference is pertinent and I have asked Alex Gonzalez and Rodrigo Iturrieta to help me extract and post the pertinent segment. Of course the entire dialogue is worth watching, there are many insightful remarks.
This dialogue was streamed live on Apr 12, 2014
http://youtu.be/WRkOYz0dtHw (this is the link to the entire dialog)
For the launch of “Berkeley Talks,” the new speaker series by Cal Performances and UC Berkeley, Chancellor Nick Dirks will gather with four of UC Berkeley’s Nobel Laureates to moderate an enlightening dialogue on the role of science in modern society and how this esteemed panel would apply scientific methods to approach the complex global issues we are dealing with today.
http://www.berkeley.edu
Current status and recommendations for control LW and RAB 4-10-13
Research and field trials in Florida show some hope but no cure. The situation today has gotten worse but they have something going for them which unfortunately the California avocado industry lacks: An all inclusive WORK GROUP composed of researchers from different fields, not only 3 entomologists and one pathologist that are very competent at what they do but the task is great and solutions are not likely to be found in the near future.
Look at the slides in the presentation and see the degree of effort and the extent of real success. The LW disease is much more severe than the Fusarium die back we are experiencing in California. I believe the current California experience is a prelude to what we could face.
Current status and recommendations for control LW and RAB 4-10
Do ambrosia beetles practice eusociality and maybe even altruism? Can we expect delayed dispersal and therefore have a clearer understanding of their population dynamics?
A short explanation from Rice university course Bios321 on animal behavior. “Many eusocial insects, including ants, bees, and wasps, are haplodiploid. Therefore, each female has two alleles at a locus, while each male has only one. This leads to a different kin relatedness than that which diploid species exhibit. For example, whereas a diploid female is related to her sister only 1/2, a haplodiploid female is related to her sister 3/4. Eusocial insects are recognized by three main characteristics:
1. The mother, along with individuals that may or may not be directly related, conducts cooperative care of young.
2. A reproductive division of labor evolves from sterile castes which often have certain propensities or characteristics associated with helping behavior.
3. There is an overlapping of generations which allows for the older generations of offspring to help related, younger generations.
The relatedness differences in haplodiploid species lead to differences in their display of kin selected behavior as compared to diploid species. On the basis of kin selection, eusocial females would be expected to prefer to help their mothers raise their sisters, increasing their indirect fitness, rather than concentrating on increasing their direct fitness by raising their own offspring.”
Katharina Peer and Michael Taborsky published in Behavioral Ecology and Sociobiology 2006 a very intriguing paper “Delayed dispersal as a potential route to cooperative breeding in Ambrosia beetles.” The authors are from the Department of Behavioral Ecology, Institute of Zoology at the University of Berne, Switzerland. The authors are interested in the evolution of cooperative breeding and social organization. Their ideas may or may not fit the Shot Hole Borer we have encountered in California but their experiments with Xyleborinus saxeseni (the same insect which was found recently in an avocado orchard in Bonsall causing symptoms similar to the ones caused by the SHB) worth looking into.
The abstract and discussion reflect on the SHB and similar experiments should be conducted in California as well.
Abstract
“Xyleborini are a species-rich tribe of ambrosia beetles, which are haplodiploid and typically mate among siblings within their natal brood chamber. Several characteristics of this tribe would predict the evolution of higher levels of sociality: high genetic relatedness within galleries due to inbreeding, high costs of dispersal and the potential benefit of cooperation in brood care within the natal gallery (e.g. by fungus gardening, gallery extension, offspring feeding and cleaning). However, information on the social system of these beetles is very limited. We examined the potential for cooperative breeding in Xyleborinus saxeseni by monitoring dispersal in relation to brood size and
composition. Results show that adult female offspring delay dispersal despite dispersal opportunities, and apparently some females never disperse. The females’ decision to stay seems to depend on the presence of eggs and dependent siblings. We found no indication that female offspring reproduce in their natal gallery, as colonies with many mature daughters do not contain more eggs than those with few or no daughters. There is a significant positive relationship between the number of females present and the number of dependent siblings (but not eggs), which suggests that cooperative brood care of female offspring raises colony productivity by improving survival rates of immatures. Our results suggest that cooperative breeding is likely to occur in X. saxeseni and possibly other xyleborine species. We argue that a closer look at sociality within this tribe may yield important information on the factors determining the evolution of cooperative breeding and advanced social organization.”
Discussion
Our results show that adult females of X. saxeseni delay dispersal from their natal galleries after reaching adulthood, which is one of three key decisions an individual has to take in a social trajectory towards cooperative breeding. Furthermore, the data suggest that females do not reproduce
in their natal gallery and that their presence enhances gallery productivity, which indicates helping behaviour.
In X. saxeseni, dispersal occurs (and hence is possible) at any time during summer and fall. However, throughout the year, a substantial number of adult female offspring remains in their natal gallery. The presence of dead females within galleries indicates that some individuals may entirely refrain
from dispersal. Regardless whether the death of these females was caused by disease or other causes, they did not disperse, although they were physically ready to do so. Hosking (1972) also reported that in 10% of all galleries, dead individuals were present after completion of dispersal, without giving information on the proportion of dead females per gallery.
What is the reason that females delay dispersal after reaching sexual maturity? They might need to feed on ambrosia for some time after emergence to achieve sclerotization (as suggested by McNee et al. 2000 for phloem-feeding bark beetles). However, this would not explain the high proportion of dark (i.e. sclerotized) females in the colony (see Appendix). A further possibility would be that females accumulate energy reserves before dispersal. We have no information about body condition and dispersal success in X. saxeseni, but a lab study of a closely related species (Xylosandrus germanus) revealed that females successfully found new galleries without consuming food in their natal gallery after emergence from the pupal stage (Peer and Taborsky 2005). Finally, it is unlikely that adult female offspring usually gain considerable direct fitness benefits through individual reproduction, as there was no positive relationship between the number of females and the number of eggs laid in a gallery. Data on ovarian development of adult female offspring are required to test this assumption, but
preliminary results from dissections show that dispersing females usually do not have developed ovaries (Biedermann, personal communication). Only a single, very large colony (with a total brood size of 291) contained a substantially larger number of eggs than all others, indicating an exceptional case where egg laying by female offspring may have occurred. As there are no obvious morphological differences between females (unpublished data), totipotency of females and some flexibility of the breeding system can be assumed.
Most galleries with adult female offspring also contained by their adult sisters (see Appendix). Our data suggest that dispersal starts when the production of new offspring ceases (i.e. when eggs and freshly hatched larvae are missing). We have no information about the cause of termination of egg laying, but it is possible that dehydration of the wood leads to deterioration of fungus, which will reduce the survival prospects of newly produced offspring. Fischer (1954) reported dispersal of X. saxeseni from logs that were dehydrated due to storage conditions, whereas there was no dispersal when logs were stored on moist ground. A similar situation was described for a drywood termite species: diminished resource availability resulted in helpers changing their tactic and becoming dispersing
reproductives (Korb and Lenz 2004). After the onset of dispersal from a gallery had started in X. saxeseni, the number of dependent offspring still present in the gallery was negatively related to the number of dispersers. This correlation may suggest that dispersal decisions depend on the amount of help needed in the natal gallery, but it may also be a fortuitous side effect if newly emerged adults
remain in the nest for some other reason, and the number of dependent brood declines due to colony aging during the same time period. However, any coincidence between female dispersal and the number of siblings in need of help provides opportunities for positive fitness effects owing to cooperation.
Positive effects of cooperative brood care are suggested by the significant relationship between the number of females in a gallery and the number of larvae and pupae. As there is no correlation with egg number, this suggests that adult female offspring generally do not produce own offspring but instead raise the probability of sibling survival. Colony size was not associated with colonization density, which makes it unlikely that site quality rather than the presence of females was responsible
for the described relationship. Provided this interpretation will be confirmed by future studies, X. saxeseni can be viewed as a communal (cooperation in brood care) or cooperative breeder (alloparental brood care), following the classification of Crespi and Choe (1997).
There are several potential tasks through which females may contribute to colony success. The ambrosia
fungus is cultivated on the surface of the gallery walls (Hosking 1972; Kirkendall et al. 1997). Excavation and enlargement of the brood chamber will increase the space and food resources available for larvae, thus creating benefits for relatives without increasing local competition. Enlargement of the gallery by adult offspring has been suggested for a number of xyleborine species (Saunders et al. 1967; Gagne and Kearby 1979; Schneider 1987; Merkl and Tusnadi 1992) including X. saxeseni (Hopkins 1898; Fischer 1954). In addition, ambrosia growth has to be
controlled so that the fungus will not overgrow the whole contribute to colony success. The ambrosia
fungus is cultivated on the surface of the gallery walls (Hosking 1972; Kirkendall et al. 1997). Excavation and enlargement of the brood chamber will increase the space and food resources available for larvae, thus creating benefits for relatives without increasing local competition. Enlargement of the gallery by adult offspring has been suggested for a number of xyleborine species (Saunders et al. 1967; Gagne and Kearby 1979; Schneider 1987; Merkl and Tusnadi 1992) including X. saxeseni (Hopkins 1898; Fischer 1954). In addition, ambrosia growth has to be controlled so that the fungus will not overgrow the whole chamber, and cropping by females or special secretions may play an important role (Hadorn 1933; Batra 1966). Finally, eggs, larvae and pupae have to be cleaned, and feces and other debris must be removed from the gallery (Kingsolver and Norris 1977). Help by adult female offspring may allow the foundress to invest more energy into egg laying.
The contribution of female helpers needs to be quantified by behavioural observations in future studies of X. saxeseni. Direct observations in the field are impossible due to the concealed lifestyle of Xyleborini, but observations may be possible through cultivation in artificial medium in the lab (e.g. Roeper et al. 1980; Bischoff 2004). We have been able to breed and observe a closely related species in artificial medium (X. germanus; Peer and Taborsky 2004), where adult female offspring were found to spend a considerable proportion of time on cleaning behaviour before dispersal (Bischoff 2004). Unfortunately, lab cultures of X. saxeseni were much less successful. Extensive attempts to optimize the culture medium have been minimally successful, and first qualitative observations confirmed that adult female offspring do indeed tend fungi in their natal gallery (P. Biedermann, personal communication).
Which factors may be important in the evolution of delayed dispersal and cooperative brood care in X.
saxeseni and other Xyleborini? If population regulation is locally plastic, i.e. more altruistic patches consisting of cooperative individuals are able to sustain higher densities, limited dispersal and inbreeding can favour altruism (e.g. Taylor 1992a,b; Mitteldorf and Wilson 2000). This situation applies to the Xyleborini, as an enlargement of brood chambers by adult offspring would permit larger
brood sizes. Inbreeding strongly affects population structure by decreasing within-family variance and selection, whereas increasing between-family variance (Wade 1980). Therefore, inbreeding is predicted to enhance the evolution of social behaviour through group selection (see also Wilson 2001). In line with this prediction, intense inbreeding has been found at the origin of eusociality in gall-inducing thrips (Chapman et al. 2000), and eusocial aphid colonies constitute a single clone because they are derived from a single foundress (e.g. Aoki 1977). Similarly, eusocial naked mole rats, social spider
mites and social spiders are characterized by high levels of inbreeding (Reeve et al. 1990; Smith and Hagen 1996; Saito 1997). In Xyleborini, levels of inbreeding are likely to be extremely high owing to their mating system (e.g. inbreeding coefficients of about 0.9 in X. germanus, own unpublished genetic data), probably comparable to those of eusocial thrips. Because of these high levels of inbreeding, which reduce relatedness asymmetries caused by haplodiploidy and increase overall relatedness, there may be little or no conflict over reproduction within xyleborine colonies.
The costs and benefits associated with the decisions of dispersal, individual reproduction and helping are largely determined by ecological factors. In X. saxeseni, constraints on individual reproduction are probably severe because a risky dispersal flight is required, and finding a suitable host location is uncertain. In addition, our data suggest that already-initiated galleries have a failure rate of 80%. Hosking (1972) also reported very high failure rates (40–60%). It remains to be determined whether this rate differs between xyleborine species. X. saxeseni appears to be particularly selective regarding the required condition of host trees: it preferentially colonizes very recently dead trees that are often still standing (personal observation). This apparent selectivity may decrease the
chances of finding a suitable host. Furthermore, the rather deep penetration of the entrance tunnel into the wood compared to other temperate Xyleborine species may require large initial investment for gallery construction and thus increase the cost of dispersal.
In ambrosia beetles, potential benefits of helping in the natal gallery are associated with the cultivation of fungus. This is a universal habit of all xyleborine species, and cooperative breeding may be a widespread phenomenon among them. A critical ecological factor determining the social system is probably gallery longevity: if brood chambers persist long enough to allow overlap between immature and mature offspring, helping in the natal gallery can be a profitable alternative to dispersing (Kirkendall et al. 1997). The galls of eusocial, gall-forming thrips are longer-lived than those of nonsocial species (Crespi and Mound 1997). The only species of ambrosia beetle that has been suggested to be eusocial, Austroplatypus incompertus, is special among these beetles, as it attacks live trees, and a colony may persist more than 30 years within a living tree (Kent and Simpson 1992). X. saxeseni has been reported to sometimes attack live trees (Hopkins 1898; Fischer 1954), and its entrance tunnels can lead several centimetres into the inner wood of a tree. This is likely to enhance the
temporal stability of the brood chamber for two reasons: dehydration proceeds from the periphery towards the centre of a log, and thus, fungus growth in deeply excavated burrows may be maintained for a longer period of time. Furthermore, the insulating effects of the wood will protect the brood chamber from very low temperatures during winter, so that overwintering is also possible for immature offspring (Fischer 1954). A prolonged phase of fungus growth and brood production together with cooperative brood care by adult offspring might also explain the unusually large brood sizes of X.
saxeseni compared to those of other European Xyleborini (Hosking 1972).
The rapid radiation of the Xyleborini together with their ecology and high sociality potential makes this tribe a promising candidate for future studies of the evolution of cooperative breeding and eusociality. The recent clarification of the phylogeny of these beetles and the coevolution with their fungal symbionts (Normark et al. 1999; Jordal et al. 2000; Farrell et al. 2001) provide an ideal background for comparative studies of the relative influence of various ecological factors on the evolution of cooperative breeding.”
Think about all these ideas, and if in your opinion there are some clues that could shed light on what we will experience in the Spring-late summer 2015. Share your thoughts, don’t be bashful.
“OUTBREEDING DEPRESSION, BUT NO INBREEDING DEPRESSION IN HAPLODIPLOID AMBROSIA BEETLES WITH REGULAR SIBLING MATING”
The SHB from LA and the SHB from San Diego are likely to meet somewhere if the encounter has not taken place already. What should we expect when these two populations meet and some outcrossing happen. Males from one population mate with females from the other population or vice versa. The experiments conducted by the authors with another ambrosia beetle Xylosandrus germanus have shown that the inbred population because of sib-mating (mating of brothers and sisters, siblings) was more fit than the outcrossed one. Apparently, since the inbreeding has been going on so long that the population has been able to purge deleterious alleles (bad recessive genes or deleterious variants of genes which were for one of several reasons have not been lost by natural selection) resulting in general in no inbreeding depression. There is a probability, if I understood the researchers correctly, for outbreeding depression. In other words there is a greater likelihood of reduced biological fitness when compared to the progeny resulting from inbreeding. The question that comes to mind and it needs to be tested, in a similar fashion as described in the article, with the two known California populations. Could this encounter lead to outcrossing depression with reduced progeny and less fit individuals. Wouldn’t such an outcome be nice or am I dreaming again? At least there is a greater chance of reducing the population and making it less fit than chipping or fumigating which can only deal with cut wood post-infestation with most likely a large number of individuals that managed to remain in the tree. (Haplodiploidy occurs with most of the ambrosia beetles. The male is haploid which results from an unfertilized egg and has only one set of chromosomes half of a female that has a double set of chromosomes, diploid.)
OUTBREEDING DEPRESSION, BUT NO INBREEDING DEPRESSION IN HAPLODIPLOID AMBROSIA BEETLES WITH REGULAR SIBLING MATING
Evolution, 59(2), 2005, pp. 317–323
KATHARINA PEER AND MICHAEL TABORSKY
Department of Behavioural Ecology, Institute of Zoology, University of Bern, Wohlenstrasse 50A,
CH-3032 Hinterkappelen, Switzerland
Abstract.
In sexual reproduction the genetic similarity or dissimilarity between mates strongly affects offspring fitness.
When mating partners are too closely related, increased homozygosity generally causes inbreeding depression, whereas crossing between too distantly related individuals may disrupt local adaptations or coadaptations within the genome and result in outbreeding depression. The optimal degree of inbreeding or outbreeding depends on population structure.
A long history of inbreeding is expected to reduce inbreeding depression due to purging of deleterious alleles, and
to promote outbreeding depression because of increased genetic variation between lineages. Ambrosia beetles (Xyleborini) are bark beetles with haplodiploid sex determination, strong local mate competition due to regular sibling
mating within the natal chamber, and heavily biased sex ratios. We experimentally mated females of Xylosandrus
germanus to brothers and unrelated males and measured offspring fitness. Inbred mating did not produce offspring
with reduced fitness in any of the examined life-history traits. In contrast, outcrossed offspring suffered from reduced
hatching rates. Reduction in inbreeding depression is usually attributed to purging of deleterious alleles, and the
absence of inbreeding depression in X. germanus may represent the highest degree of purging of all examined species so far. Outbreeding depression within the same population has previously only been reported from plants. The causes and consequences of our findings are discussed with respect to mating strategies, sex ratios, and speciation in this unusual system.
Close associations with fungi and species that consume fungal tissue = mycophagy
Biol. Rev. (1979), 54, pp. 1-21
BIOCHEMICAL IMPLICATIONS OF INSECT MYCOPHAGY
BY MICHAEL M. MARTIN
Department of Chemistry and Division of Biological Sciences,
University of Michigan, Ann Arbor, Michigan 48109, U.S.A.
This is a unique and very important review of the biochemical aspects of insects and their associate fungi. The author was correct to make the following statement 36 years ago; it still holds true today.
“Although mycophagy is widespread among insects, the biochemical requirements and consequences of this mode of nutrition have not received the attention they deserve. Indeed, a major impetus for the preparation of this review was the belief that a failure to recognize the many biochemical implications of mycophagy has led to a general lack of appreciation of its full biological significance.”
The subjects discussed in the paper:
1. Arthropod-fungal associations
2. Nutritive characteristics of fungal tissue
3. Digestive and metabolic requirements imposed on mycophagous species by the special characteristics of fungal tissue
4. Acquired digestive enzymes: a windfall of mycophagy
SUMMARY
I. Fungal tissues have high nutritive potential. Although rather similar to foliage in their over-all nutrient make-up, fungal tissues and plant tissues are very different in terms of the chemical structures of many of their constituents.
2. The major structural polysaccharides of fungal cell walls are chitin and noncellulosic p-(1,3)- and p-(1,6)-glucans. Cellulose, lignin and pectin are absent. It is not known whether chitinase and ,p-(1,3)- and p-( 1,6)-glucanases, the enzymes required for the digestion of the major fungal polysaccharides, occur widely in insects or not. (notice the letter p is supposed to be lower case of the Greek letter ‘beta’; I’ll replace it when I figure out how, sorry RH).
3. The most common fungal sterol is the 28-carbon sterol, ergosterol. The capacity to utilize this sterol by removing the methyl group at C-24 of the side chain, thereby converting it to a cholesterol derivative, is widespread among insects, including phytophagous species which do not normally consume fungal sterols.
4. Many fleshy fungi accumulate urea and ammonia in their fruiting bodies. It is not known whether mycophagous insects can utilize the nitrogen of dietary urea or ammonia for protein synthesis.
5. Fungi contain many secondary metabolites which doubtless play a role in determining host preferences in fungus-feeding species.
6. Fungi produce large amounts of several classes of enzymes which may continue to function in the gut of an insect which consumes fungal tissue or a substrate into which the fungal enzymes have been secreted.
7. Fungal enzymes acquired during feeding may contribute to the digestion of cellulose, hemicellulose and pectin in the guts of wood- and litter-feeding arthropods.
8. FungaI enzymes acquired during feeding may contribute to the digestion of chitin and non-cellulosic ,p-glucans in the guts of arthropods which feed on fungal sporophores or which otherwise restrict their diets largely to fungal material.
9. Fungal phenol oxidases acquired during feeding may augment an insect’s capacities for detoxification.
Learning about beetles, an educational series for those who want to learn more.
In my efforts to understand and try to come up with ideas for potential solutions to how to deal with the devastating effects of ambrosia beetles present in California avocado groves and others which are on their way, I find it necessary to study the subject of beetles which has been extensive yet limited because of the devastating consequences of their feeding and breeding pathways.
I know that many are reluctant to read material especially if the subject is foreign and boring. In my view, the less we know the more we need to investigate and research. In the case of the California avocado growers time is against us so I find it necessary to spend hours reviewing whatever I can get my hands on to help me have a more complete picture of the enemy. I have decided to share some of what I consider relevant to shedding light on this not too sudden invasions by beetles all around the United States, mainly by bark beetles and specifically the ambrosia beetles that are pertinent to the sustainability of our industry.
If you come up with ideas, however strange but practical, write to this blog to encourage discussion. Your views are as good as any given the limited knowledge base particularly how to deal with these plagues under the diverse growing conditions. There are many variables, some more important than others, that must be considered: trees, beetles and fungi are living organisms which interact with each other in their natural setting mostly in beneficial ways. Once the beetles become invasive in other settings in forests and agriculture the tripartite interaction could become detrimental.
Watch for new material and Happy Holidays.
Reuben Hofshi
“Native ambrosia beetles generally attack weakened or stressed trees; however, healthy trees are frequently attacked by exotic species” See the quotes regarding Xyleborinus saxeseni which is the beetle found recently in avocado orchards in Bonsall, San Diego County causing attack symptoms similar to the SHB.
I have been researching various aspects that can shed light on the behavior of the ambrosia beetles attacking our groves. The quote from the article by D.R. Coyle et al. represents some of my observations and thinking and that is that the ambrosia beetles will be attracted to healthy trees, that are well fertilized and irrigated and that not all trees of the same species are equally susceptible. Some of the quotes could be repetitious but they will serve as a reminder of the research that needs to be conducted in California regarding the behavior of the SHB and its fungal symbionts. All of the three observations could tell us what we should expect in the near future and that is that the beetles are attracted to healthy trees which are well irrigated and fertilized (our well cared for avocado trees) and that not all varieties are equally attacked:
“Of four tree species in the plantation, eastern cottonwood, Populus deltoides Bartram, was the only one attacked, with nearly 40% of the trees sustaining ambrosia beetle damage. Clone ST66 sustained more damage than clone S7C15. ST66 trees receiving fertilization were attacked more frequently than trees receiving irrigation, irrigationfertilization, or controls, although the number of S7C15 trees attacked did not differ among treatments. The study location is near major shipping ports; our results demonstrate the necessity for intensive monitoring programs to determine the arrival, spread, ecology, and impact of exotic scolytids.”
“Native ambrosia beetles generally attack weakened or stressed trees; however, healthy trees are frequently attacked by exotic species.”
Ambrosia Beetle (Coleoptera: Scolytidae) Species, Flight, and Attack on Living Eastern Cottonwood Trees
D. R. COYLE, D. C. BOOTH, AND M. S. WALLACE
USDA Forest Service, Southern Research Station, New Ellenton, SC 29809
“NEARLY 50% OF EXTINCT or imperiled species in the United States were caused, in part, by invasive species (Wilcove et al. 1998). Pimentel et al. (2000) suggest that invasive species cost the U.S. economy $138 bil- lion annually. There are >400 invasive insect species in U.S. forests, encompassing a wide range of feeding guilds
(Mattson et al. 1994). Bark and ambrosia beetles (Coleoptera: Scolytidae) can be particularly hard to detect because of their cryptic lifestyle and the difficulty in effectively monitoring their populations in remote areas. Several invasive scolytids are of concern because of their unknown damage potential (Atkinson et al. 1988b, Mizell et al. 1994, Bright and Rabaglia 1999, Vandenberg et al. 2000, Haack 2001, Schiefer and Bright 2004). In the absence of effective monitoring, exotic species may persist undetected for many years before discovery (Liebhold et al. 1995, Humble 2003). Ambrosia beetles, with the exception of a short flight period, spend their entire life within a woody stem (Rudinsky 1962). Native ambrosia beetles generally attack weakened or stressed trees; however, healthy trees are frequently attacked by exotic species (Rudinsky 1962, Wood 1982b, Kuhnholz et al. 2001).”
ABSTRACT
In spring 2002, ambrosia beetles (Coleoptera: Scolytidae) infested an intensively managed 22-ha tree plantation on the upper coastal plain of South Carolina. Nearly 3,500 scolytids representing 28 species were captured in ethanol-baited traps from 18 June 2002 to 18 April 2004. More than 88% of total captures were exotic species. Five species [Dryoxylon onoharaensum (Murayama), Euwallacea validus (Eichhoff), Pseudopityophthorus minutissimus (Zimmermann), Xyleborus atratus Eichhoff, and Xyleborus impressus Eichhoff]) were collected in South Carolina for the first time. Of four tree species in the plantation, eastern cottonwood, Populus deltoides Bartram, was the only one
attacked, with nearly 40% of the trees sustaining ambrosia beetle damage. Clone ST66 sustained more damage than clone S7C15. ST66 trees receiving fertilization were attacked more frequently than trees receiving irrigation, irrigation fertilization, or controls, although the number of S7C15 trees attacked did not differ among treatments. The study location is near major shipping ports; our results demonstrate the necessity for intensive monitoring programs to determine the arrival, spread, ecology, and impact of exotic scolytids.”
“We hypothesized that the majority of captured beetles would be exotic species (Kovach and Gorsuch 1985) because ports in South Carolina provide opportunities for exotic scolytids to establish after being imported in ballast or other wood products (Haack 2001). We also hypothesized ambrosia beetle fight patterns would peak in spring and late summer, as documented previously (Roling and Kearby 1975, Turnbow and Franklin 1980, Atkinson et al. 1988a, Weber and McPherson 1991). Finally, because the incidence and severity of pest damage can differ among P. deltoides clones and resource amendment treatments (Coyle 2002, Herms 2002, Huberty and Denno 2004, Coyle et al. 2005), we hypothesized that the incidence of ambrosia beetle attack would differ between two P. deltoides clones and would be highest in trees receiving irrigation and fertilization amendments.”
“We captured 3,495 scolytids, mostly tribe Xyleborini, over 94 wk (Table 2). Seven of the 28 species were captured every year. Nine exotic species made up 88% of the total specimens collected. Xyleborinus saxeseni (Ratzburg) (Xyleborinus saxeseni the Pinhole Borer, is the “other” beetle found recently in Bonsall attacking avocado limbs and were mistaken for the SHB because of tree symptoms. ) accounted for 64% of total trap captures alone (Table 2). X. saxeseni, X. crassiusculus, and Hypothenemus spp. accounted for nearly 85% of all specimens collected. Twenty species were represented by 20 individuals (Table 2).
Flight Patterns. VERY IMPORTANT
“Beetle flight was fairly constant from late June through November 2002 (Fig. 1A). Noticeable decreases in flight occurred when temperatures or humidity were unusually high. The decreases in flight activity in mid-August and mid-September 2003 corresponded to mean temperatures 28C and relative humidity 94%, respectively. Activity ceased
from late November 2002 until the end of January 2003, when beetles occurred in very small numbers (0.04 beetles trap1 d1). Beginning in late February 2003, flight activity began to increase steadily (Fig 1A). A substantial rain (6.9 cm) on 20 March 2003 likely reduced trap catches just before their greatest levels (13 beetles trap1 d1) on 1 April 2003. Heavy rain fell during the first 2 wk of April 2003 (14.6 cm), and again on 25 April 2003 (40.9 cm), decreasing trap captures a final time (Fig. 1A) before their natural decline. Flight activity remained consistent throughout
the remainder of summer and fall, until ceasing completely in the beginning of December 2003 (Fig. 1A). Beetles first occurred in mid-March 2004, much later than in 2003, and exhibited consistent flight activity until we stopped trapping in April 2004.”
Attack Incidence.
There is a wide range of susceptibility to pests as well as pest host preference among P. deltoides clones (Coyle et al. 2005). For example, clones in this plantation differed in their susceptibility to T. lobulifera (Coyle 2002). However, no studies have compared ambrosia beetle attack incidence on Populus clones, because attacks on healthy hosts are a relatively new phenomenon (Kuhnholz et al. 2001). Clone ST66 was attacked more than clone S7C15 (Fig. 2), even though diameter between clones and among treatments was nearly identical (Coyle and Coleman 2005). However, we cannot determine whether this was because of host susceptibility or beetle preference.
The effect of resource amendments such as irrigation and fertilization on tree susceptibility to pests is under debate (Herms and Mattson 1992, Koricheva et al. 1998, Herms 2002, Huberty and Denno 2004). The growth-differentiation balance hypothesis (GDBH) for a resource-based balance between plant growth and defense (Herms and Mattson 1992) best explains the interaction between resource availability and host susceptibility. If resource availability limits growth, increases in resource availability will stimulate plant growth at the expense of defense. Our data suggest
that the GDBH may differ among genotypes, because beetle attack incidence did not differ among resource amendment treatments in clone S7C15, yet ST66 trees receiving fertilization were attacked the most. The synthesis of Lorio (1986) of the ecology of the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), provides a compelling argument in support of the GDBH for southern pines. Attacks by Scolytidae are greatest in the spring when trees are allocating most of their resources to new growth and not defense. However, bark and ambrosia beetle attack rates dwindle throughout the summer as tree growth levels off and resources are
converted into defensive compounds (except for an occasional peak in late summer or fall, generally corresponding to a defensive compounds (except for an occasional peak in late summer or fall, generally corresponding to a drought period and subsequent tree stress). White pine weevil, Pissodes strobi (Peck), attack rates on spruce, Picea glauca (Moench) Voss P. engelmannii Parry ex. Engelmann, also increased as fertilization rates increased (vanAkker et al. 2004). Fertilization increased plant material available for weevil feeding, but it did not affect induced resistance
capabilities. With only two irrigation and fertilization treatments, this study was not designed to test the GDBH (Wilkens 1997, Stamp 2004), nor was that its original purpose (Coleman et al. 2004). Although growth losses to weevils were less than gains from fertilization, additional pest management tactics may be required if fertilization is used as a silvicultural treatment.”
Avocado is an evergreen tree and has a significant summer flush which is a strong sink for nutrients and also the season when heat stress in California is common. Therefore late summer flights are very likely to take place and could potentially exceed the flights during the spring flush in my opinion. For further discussion on the subject of “growth-differentiation balance hypothesis”
stamp 04 gdb hypothesis OIKOS 107:2 (2004). 439-448
Can the growth differentiation balance hypothesis be tested rigorously?
Nancy Stamp, Dept. of Biological Sciences, Binghamton Univ. State Univ. of New York, Binghamton, NY 13902- 6000, USA (nstamp@binghamton.edu).
ABSTRACT
ABSTRACT
“The growth differentiation balance (GDB) hypothesis (as elaborated by Herms and Mattson) provides a framework for examining the impact of a resource gradient on the constant trade off between growth and differentiation in cells and tissues of plants, in particular with the consequences for plant defense. The GDB hypothesis, which is the most mature of the hypotheses of plant defensive levels, has not been tested directly. Examination of the requirements for a rigorous test indicates that, like the other hypotheses of plant defense, it cannot be tested directly. Furthermore, rigorously testing the primary derivative hypotheses, while possible, would require considerable methodological effort, on a scale not previously attempted for tests of plant defense, which is likely to discourage researchers, and
understandably so, even though the GDB hypothesis warrants methodical investigation due to its potential explanatory power.”
Although farther removed from the abstract model (i.e. the GDB
framework), other derivative hypotheses can be tested, but doing
so will require thoughtful consideration and acknowledgement of
that. Study of a few carefully chosen systems (i.e. plant species)
may provide considerable insight and potentially useful refinement
of the GDB framework.
Are you interested in understanding the bark beetles and fungus symbioses?
Click on the Attachment below; this is a very good current review by Dr. Diana Six in Insects 2012, 3, 339-366.
Review
Ecological and Evolutionary Determinants of Bark Beetle — Fungus Symbioses
Abstract:
Ectosymbioses among bark beetles (Curculionidae, Scolytinae) and fungi (primarily ophiostomatoid Ascomycetes) are widespread and diverse. Associations range from mutualistic to commensal, and from facultative to obligate. Some fungi are highly specific and associated only with a single beetle species, while others can be associated
with many. In addition, most of these symbioses are multipartite, with the host beetle associated with two or more consistent partners. Mycangia, structures of the beetle integument that function in fungal transport, have evolved numerous times in the Scolytinae. The evolution of such complex, specialized structures indicates a high degree
Ectosymbioses among bark beetles (Curculionidae, Scolytinae) and fungi (primarily ophiostomatoid Ascomycetes) are widespread and diverse. Associations range from mutualistic to commensal, and from facultative to obligate. Some fungi are highly specific and associated only with a single beetle species, while others can be associated
with many. In addition, most of these symbioses are multipartite, with the host beetle associated with two or more consistent partners. Mycangia, structures of the beetle integument that function in fungal transport, have evolved numerous times in the Scolytinae. The evolution of such complex, specialized structures indicates a high degree
of mutual dependence among the beetles and their fungal partners. Unfortunately, the processes that shaped current day beetle-fungus symbioses remain poorly understood. Phylogeny, the degree and type of dependence on partners, mode of transmission of symbionts (vertical vs. horizontal), effects of the abiotic environment, and interactions
among symbionts themselves or with other members of the biotic community, all play important roles in determining the composition, fidelity, and longevity of associations between beetles and their fungal associates. In this review, I
among symbionts themselves or with other members of the biotic community, all play important roles in determining the composition, fidelity, and longevity of associations between beetles and their fungal associates. In this review, I
provide an overview of these associations and discuss how evolution and ecological processes acted in concert to shape these fascinating, complex symbioses.
Advice to CAC “Ask and it will be given to you; seek and you will find; knock and the door will be opened for you.” Matthew 7:7
The California avocado industry is being challenged on several fronts. Two individuals, Tom Bellamore and Ken Melban have risen to the occasion and have been working hard facing these challenges. The most recent challenge has been the Shot Hole Borer invading avocado groves in San Diego County. To deal with this plague is a stressful task by all means; it is an invasive complex of an ambrosia beetle with its fungal symbionts. There is not much known about this complex and surely there is no known treatment to eliminate the beetle from our groves. The industry has to basically start from scratch to come up with management strategies. CAC management feels the pressure and the necessity to “do something” even though some of the “somethings” are likely to result in additional costs for the growers. With limited success growers might feel that CAC is not doing enough. This is not the case. CAC is trying but the prognosis for significant success is slim. My fear is that even if some growers are successful at keeping their groves pest-free by careful removal of infested branches, others, faced with the additional costs and the grim perspective, elect to leave their groves infested and untreated to serve as a source of beetles to invade other groves. This is what is currently taking place in Florida as some of the photos from a previous blog depict.
To take away some of the burden I have suggested forming an international taskforce to address all aspects of invasive ambrosia beetle and most importantly produce results that growers can practically use. Like in some other situations CAC believes it can do it alone. Well I think that in this case they are mistaken; this problem is bigger than us and needs a global approach. We need to join forces with the Israelis who have been fighting this war for several years, we need to work with the Floridians who are battling a different ambrosia beetle and we need to learn from others worldwide who are experts in ambrosia beetles. The taskforce I have proposed would seek to bring all these parts together into a cohesive effort to develop management strategies for our industry.
I read comments by Rabbi Yaakov Lieder about winning the battle but losing the war: “King Solomon, said: “Without strategies a nation will fall, but salvation lies in much counsel” (Proverbs 11:14). To me, this means we are so caught up by our egos and our opinions that we may miss some very important points and end up losing more than we gain.”
“Remember that asking for advice does not show a weakness on your part, but rather strength that you are smart enough to realize that you are not perfect and that because you are so emotionally involved, you are seeking independent advice.”
Why did I quote Rabbi Lieder? His message is similar to mine: Get off the high horse and let’s put all our and others’ efforts together so we can both win the battle and win the war! “We are so caught up by our egos and our opinions that we may miss some very important points and end up losing more than we gain.” King Solomon is even more to the point: “Without strategies a nation will fall, but salvation lies in much counsel”
California Avocado Comments 