Effect of rearing Cactoblastis cactorum on an artificial diet on the behavior of Apanteles opuntiarum

Authors: VARONE, LAURA - Fuedei; GONALONS, CAROLINA - Fuedei; FALTLHAUSER, ANA - Fuedei; GUALA, MARIEL - Fuedei; WOLAVER, DANIELLE - Florida Department Of Agriculture And Consumer Services; SRIVASTAVA, MRITTUNJAI - Florida Department Of Agriculture And Consumer Services; Hight, Stephen

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2020
Publication Date: 1/16/2020
Citation: Varone, L., Gonalons, C.M., Faltlhauser, A.C., Guala, M.E., Wolaver, D., Srivastava, M., Hight, S.D. 2020. Effect of rearing Cactoblastis cactorum on an artificial diet on the behavior of Apanteles opuntiarum. Journal of Applied Entomology. 144:278-286. https://doi.org/10.1111/jen.12731.
DOI: https://doi.org/10.1111/jen.12731

Interpretive Summary: A small parasitic wasp (parasitoid) is being assessed as a potential biological control agent of the Argentine cactus moth that is attacking and destroying prickly pear cactus in the southern USA. Rearing the parasitoid currently relies on feeding the host caterpillars fresh cut pads of prickly pear, a timely, costly, and messy process. Unfortunately, caterpillars reared on artificial diet are not readily accepted as hosts by parasitoids. Scientists with USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology, Tallahassee, Florida, in collaboration with scientists at the Argentine Foundation for the Study of Invasive Species, and the Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Gainesville, Florida, conducted a series of trials with varying environmental feeding ques to improve the rate of attack by parasitoids on diet-reared caterpillars. The presence of cactus pieces when parasitoids and hosts were placed together did lead to higher parasitism of diet-fed caterpillars. Parasitoids also attacked more cactus-fed than diet-fed caterpillars. The laboratory rearing protocol of the parasitoids has incorporated the addition of frass from cactus-fed larvae and a piece of cactus during parasitoid mating, and the switching of diet-fed caterpillars onto cactus pads at least one day before exposing them to female parasitoids. The new protocols result in a savings in rearing costs and the ability to use an inexpensive diet to feed early stages of the caterpillars to produce the parasitoids year-round which improves the biological control program for control of the Argentine cactus moth.

Technical Abstract: Cactoblastis cactorum’s unintended arrival to Florida and its expansion in North America represents a threat to Opuntia-based agriculture and natural ecosystems in USA and Mexico. Apanteles opuntiarum attacks C. cactorum and has potential as a biocontrol agent due to its specificity, wide distribution and occurrence. Laboratory rearing methods utilizing excised cladodes for C. cactorum as host larvae of A. opuntiarum were developed but require a continuous supply of cactus with a risk of microorganisms compromising the rearing. For parasitoids, host associated olfactory cues are the most important signals leading to host location, including odor of host metabolic sub products like feces, and chemicals emitted by the attacked plant. Little attention has been paid to behavioral differences of parasitoids in the presence of hosts reared on artificial diet, so the objectives of the present work were to determine the effect of the meridic diet for C. cactorum on parasitoid ability and behavior, and to determine if prior experience influences the response of A. opuntiarum to hosts. Parasitism rate and sex ratio were evaluated using cladodes or meridic diet as larval food source. Behavioral experiments also evaluated the effect of prior experience (larvae or frass from larvae fed on cactus or diet) on host searching, encounter, and attack. Parasitism behavior of A. opuntiarum was negatively affected by the use of meridic diet to feed host larvae. The most influential factor that elicited excitatory behavioral responses was the type of substrate used at the time of oviposition, not the prior experience. However, a slight effect was observed due to the previous encounter with host frass, indicating a relevant stimulus for host location and acceptance. For laboratory mass rearing procedures of A. opuntiarum, we recommend adding frass from cactus fed larvae and a piece of cactus during parasitoid mating to maximize parasitism rates and percentage of female offspring.