Diachasmimorpha longicaudata and D. kraussii (Hymenoptera: Braconidae), potential parasitoids of the olive fruit fly

The olive fruit fly, Bactrocera oleae (Tephritidae), is a significant threat to California's olive industry. As part of a classical biological control program started in 2002, the parasitoids Diachasmimorpha kraussii and D. longicaudata (Hymenoptera: Braconidae) were imported to California from laboratory colonies in Hawaii. Studies on their biology and behavior as parasitoids of the olive fruit fly were conducted in quarantine. Both species tend to oviposit into 2nd and young 3rd instars, with the offspring completing development in the flies’ puparia. Most eggs are deposited in the first two weeks of adult life. Observed lifetime fecundity was low, possibly as a consequence of the relatively poor quality of the harvested olives used as a host substrate. Both pre-imaginal development and adult longevity were limited at constant temperatures above 30°C, which may indicate that these species will have difficulty establishing in the warmest regions of California.     

Combining pheromone-baited and food-baited traps for insect pest control: Effects of additional control by parasitoids

Two age-structured population dynamic models are analyzed in which pheromone-baited trapping and food-baited trapping are used simultaneously to eradicate an insect pest. The pest species is assumed to be under partial control by a host-specific parasitoid species. The two models assume that density-dependent population regulation is accomplished either by host larval competition or by means of oviposition interference among the parasitoids. The two trap types interact in a positive synergistic manner and this combination appears to be very promising as a useful combination of pest control methods. Several features of the system are examined; the feature which appears to cause the greatest problem is the possibility of the parasitoids being attracted to the pheromone or the food traps. In either case, the degree of attraction does not have to be very great to undermine the control effort. It is seen that food trapping becomes indispensible if host pheromone is used by the parasitoids as a host-locating kairomone. If odor in the food traps is used by the parasitoids as kairomone, then the situation appears more optimistic, as the reduction in efficiency of the food traps appears much less than with the pheromone traps when pheromone acts as kairomone.     

Effect of Diachasmimorpha tryoni on two non-target flowerhead-feedingtephritids

Laboratory tests were conducted to evaluate the possible effect of a deliberately introduced fruit fly parasitoid, Diachasmimorpha tryoni, on 2 non-target flowerhead-feeding tephritid flies,Trupanea dubautiae and Ensina sonchi. The former is an nativecomposite endemic Hawaiian tephritid which feeds on flowerheads of the native composite shrub, Dubautia raillar dioides; the latter is an inadvertently introduced tephritid infesting flowerheads of the exotic weed, Sonchus oleraceus. Gravid females of D. tryoniwere confined in test cages with field-collected D.raillardioides and S. oleraceus flowerheads infested with late instars of T. dubautiae and E. sonchi,respectively. D. tryoni showed low levels of visiting and probing responses to D. raillardioides flowerheads and relatively higher responses to S. oleraceus flower heads in both the presence and absence of the parasitoid's normal host, the Mediterranean fruit fly, Ceratitis capitata. With 72-h exposure to D. tryoni, 13.9 and 2.6% of T. dubautiaewere attacked by test parasitoids in the absence and presence of C.capitata in the test cage, respectively; while 56.8 and34.2% of E. sonchi were attacked. In contrast, 94.0 and84.0% of C. capitata larvae presented in screened disheswith diet in test cages were attacked by D. tryoni in testswith T. dubautiae and E. sonchi, respectively. Attackof D. tryoni on flowerhead-feeding T. dubautiae andE. sonchi resulted in significant reduction in the emergence ofadult flies, especially in the absence of the parasitoid's normal host.While 8.8–12.8 adult D. tryoni per test (both males andfemales) successfully emerged from medflies, no adult D. tryoniprogeny emerged from T. dubautiae, and only 3 deformed males ofD. tryoni (much smaller than the normal wasp) emerged fromE. sonchi. The relevance of these findings to the safety offuture biological control programs against tephritid pests is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of Fopius arisanus as a biological control agent for the olive fruit fly in California

1 The egg‐prepupal parasitoid Fopius arisanus (Hymenoptera: Braconidae) was evaluated in quarantine facilities as a potential biological control agent for the olive fruit fly Bactrocera oleae (Diptera: Tephritidae) in California, U.S.A. 2 Nontarget testing of two weed biological control agents confirmed that F. arisanus will not attack Tephritidae that feed in inflorescences or galls. It may, however, pose risks to native Tephritidae that feed in fruit. 3 Females preferentially oviposited in eggs, although first‐instar B. oleae were also attacked. Low lifetime reproductive potential and high rates of direct mortality inflicted on host eggs indicate that rearing on B. oleae may prove difficult. 4 In multiparasitized B. oleae, F. arisanus prevailed in competition against two species of larval–pupal parasitoids, Diachasmimorpha kraussii and Psyttalia concolor (both Hymenoptera: Braconidae). 5 The broad host‐range of F. arisanus with respect to fruit‐feeding Tephritidae may preclude its introduction to California, as may its low fecundity and its intrinsic competitive superiority over larva l–pupal parasitoids, which include specialists on B. oleae that are currently being introduced to California. High rates of direct mortality, however, point to potential uses in augmentative biological control. Whether or not F. arisanus is released in California, its biology as a parasitoid of B. oleae has been little studied to date and the results herein may be applied in other regions worldwide where B. oleae is a problem.     

Effects of irradiation dose rate on quality and sterility of Queensland fruit flies, Bactrocera tryoni (Froggatt)

Queensland fruit fly (Bactrocera tryoni; Q‐fly) pupae are routinely irradiated to induce reproductive sterility in adults released in a sterile insect technique programme. Although there have been some studies of how total dose influences fly quality, dose rate has not been considered. In the present study, pupae were irradiated at a target dose range of 70–75 Gy at dose rates of approximately 5, 7, 26, 57 and 80 Gy/min and were then subjected to routine IAEA/FAO/USDA quality control tests including emergence, flight ability, mortality under stress and sterility induction. No significant effects of dose rate were found on emergence or flight ability. Sterility induction was also found to be independent of dose rate, a result conforming to a ‘one‐hit’ ionizing event hypothesis. Flies irradiated at higher dose rates suffered increased mortality under stress. This appears to stem from an increased tendency to over‐shoot the target dose when irradiating at high dose rates. We recommend that, to reduce potential error in total target dose, the lowest practical dose rate be used when irradiating Q‐fly pupae for use in the sterile insect technique.     

Combining methods of insect pest control: Partitioning mortality and predicting complementarity

An age-structured population model is used as a vehicle for presenting a method for the analysis of interactions between pairs of insect pest control methods. This analysis is based on partitioning the total mortality acting on a population into its constituent components from all known sources. Pairwise critical mortality curves are then constructed which represent the combined mortality required for eradicating the pest population. Effort curves are then constructed from computing the mortality resulting from a given amount of control effort. The convolution of the critical mortality curves and the effort curves then yields the isoclines formed by the effort required of two control methods in combination to achieve eradication. This analysis allows the prediction of either synergism or interference between the control methods and also helps explain patterns observed in previous modelling of such combinations of pest control methods.     

The production, storage and viability of seeds of Acacia karroo and A. nilotica in a grassy savanna in KwaZulu-Natal, South Africa

African Acacias are often major contributors to the progressive increase in the woody component of savannas, a phenomenon commonly referred to as bush encroachment. They produce large quantities of seed and may have large soil‐stored seed banks. In Hluhluwe–Umfolozi Park, the number of adult Acacia nilotica trees per hectare far exceed that of A. karroo adults. The relative dominance is reversed in the juvenile stage with A. karroo outnumbering A. nilotica threefold outside closed woodlands. Acacia karroo trees were smaller than A. nilotica trees on average, but produced more seeds for a given basal diameter size class. Acacia karroo showed less bruchid infestation than A. nilotica at all stages of pod development. Unlike A. nilotica, a proportion of A. karroo seeds was able to germinate after bruchid attack. We detected no difference between the two species in the soil‐stored seed bank or in the viability of seeds found in the seed bank.     

Artificial diets for rearing the coconut hispine beetle,Brontispa longissima (Coleoptera: Chrysomelidae), and their suitability to two specialist parasitoids

The coconut hispine beetle, Brontispa longissima (Gestro), is a serious invasive pest that infests young unopened fronds of coconut palms (Cocos nucifera L.) in Southeast Asia. We previously developed the first artificial diet for rearing B. longissima larvae, which contained a leaf powder of young coconut fronds. Because the fronds are required for healthy growth of coconut palms, it is necessary to reduce their use for rearing the beetles. In this study, we tested two new artificial diets for the beetle larvae, which contained the leaf powders of mature coconut leaves or orchard grass (Dactylis glomerata L.). Brontispa longissima successfully developed from hatching to adulthood on both the mature coconut leaf diet and orchard grass diet. The beetles reared on the mature coconut leaf diet and orchard grass diet developed faster than those reared on the young coconut leaf diet. Fecundity and egg hatchability of beetles did not differ among the three diet treatments. We then examined the suitability of beetle larvae or pupae reared on each diet as hosts for two specialist endoparasitoids, Asecodes hispinarum Boucek and Tetrastichus brontispae Ferriere. The survival rate from oviposition to adult emergence for A. hispinarum was 43.8% in hosts reared on a young coconut leaf diet, 77.1% on a mature coconut leaf diet, and 85.7% on an orchard grass diet. For T. brontispae, the survival rate was 70.0% in hosts reared on the young coconut leaf diet, 38.1% on the mature coconut leaf diet, and 66.7% on the orchard grass diet. Our results indicate these artificial diets can be useful for rearing B. longissima and its two parasitoids, helping to reduce the costs of mass rearing these insects.